1 Technical Field
The present invention relates to stators for rotating electric machines that are used in, for example, motor vehicles as electric motors and electric generators.
2 Description of Related Art
Conventionally, there are known stators for rotating electric machines which include a hollow cylindrical stator core, a stator coil and an outer cylinder. The stator core is comprised of a plurality of stator core segments that are arranged in the circumferential direction of the stator core to adjoin one another in the circumferential direction. Further, to reduce iron loss of the stator, each of the stator core segments is formed by laminating a plurality of steel sheets in the axial direction of the stator core. The stator coil is mounted on the stator core. The outer cylinder is fitted on the radially outer surfaces of the stator core segments so as to fasten them together.
Moreover, Japanese Unexamined Patent Application Publication No. 2012-161237 discloses a method of preventing relative circumferential movement (or relative rotation) between the outer cylinder and the stator core.
Specifically, according to the method, the outer cylinder has a slit and a fastening portion for fastening the outer cylinder to the stator core. The slit radially penetrates the outer cylinder to connect the radially outer and inner surfaces of the outer cylinder. The fastening portion is formed to adjoin the slit. In manufacturing the stator, after the outer cylinder is fitted onto the radially outer surface of the stator core (or the radially outer surfaces of the stator core segments), at least part of the fastening portion of the outer cylinder is plastically deformed radially inward into a recess formed in the radially outer surface of the stator core, thereby engaging with the recess. Consequently, with the engagement between the at least part of the fastening portion of the outer cylinder and the recess of the stator core, the outer cylinder and the stator core are prevented from circumferentially moving (or rotating) relative to each other.
Further, after the at least part of the fastening portion of the outer cylinder is plastically deformed radially inward into the recess of the stator core, a radial gap may be formed between the at least part of the fastening portion and a wall surface of the recess due to springback of the fastening portion. Therefore, to prevent formation of such a radial gap, the method further includes, before the step of fitting the outer cylinder onto the radially outer surface of the stator core, a preliminary bending step in which the at least part of the fastening portion of the outer cylinder is bent radially inward by a predetermined amount.
However, with the at least part of the fastening portion of the outer cylinder bent in the preliminary bending step, the outer cylinder is press-fitted onto the radially outer surface of the stator core in the subsequent fitting step. That is, the outer cylinder axially slides on the radially outer surfaces of the stator core segments in the fitting step. Consequently, the steel sheets forming the stator core segments may be axially separated from one another by the axial sliding of the outer cylinder on the radially outer surfaces of the stator core segments.
In addition, with the preliminary bending step, the number of steps of the method is increased, thereby lowering the productivity and increasing the manufacturing cost of the stator.